Nanoscale spectroscopic investigation of impact of strain on field-effect mobility of WS2.

In this work, an in-depth study of the strain originating from the metallic pads of field effect transistors with WS₂channels are reported. Presence of tensile strain caused by Ni/Pd pads fabricated with a lift-off process is confirmed with high resolution tip-enhanced Raman and photoluminescence. This strain field appears to extend in the 1-2µm vicinity of the pads and affect the optical bandgap of the layer. The severity and the profile of the mechanical stress seems to depend on factors like device architecture, channel length, and the contact area of the pads. Results indicate that the optical response of the channel can be correlated to the field-effect mobility, both factors reflecting the quality of the crystal, and be utilized in robust assessment of mechanical stress in these devices.